Joints, also known as articulations, are classified based on their structural characteristics, i.e., based on whether the articulating surfaces of the adjacent bones are directly connected by fibrous connective tissue or cartilage, or whether the articulating surfaces contact each other within a fluid-filled joint cavity. These differences serve to divide the joints of the body into three structural classifications.

A fibrous joint is where the adjacent bones are united by fibrous connective tissue. It lacks a synovial cavity. The bones are joined by dense irregular connective tissue rich in collagen fibers. These joints allow minimal to no movement.

At a cartilaginous joint, the bones are joined by hyaline cartilage or fibrocartilage. These joints also lack synovial cavities. These joints provide more stability than fibrous joints but allow limited movement.

At a synovial joint, the articulating surfaces of the bones are not directly connected but instead come into contact with each other within a joint cavity that is filled with lubricating fluid. They also contain dense irregular connective tissue in the articular capsule. Bones in a synovial joint are often stabilized and held together by accessory ligaments. Synovial joints allow for free movement between the bones and are the most common joints of the body.

Parts of this text are adapted from Openstax, Anatomy and Physiology 2e, Section 9.1: Classification of Joints